Magnetic centrifugal device



June 19, 1956 K. M. FEIERTAG 2,751,455

MAGNETIC CENTRIFUGAL DEVICE Filed Feb. 23, 1954 ll l 1". 11

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MAGNETIC carsrnrruoar DEVICE Karl M. Feiertag, Fort Wayne, ind, assignorto Genera! Electric Sorupany, a corporation of New York ApplicationFebruary 23, 1954, Serial No. 411,671

6 Claims. (Cl. Nil-80) This invention relates to speed responsiveapparatus, and more particularly to a magnetic centrifugal device.

There are many applications for speed responsive apparatus; among theseis the function of control operable at a predetermined speed. Such acontrol is often used, for instance, in small single phase alternatingcurrent motors which are started with a main winding and a startingwinding in parallel, the starting winding being disconnected when themotor attains a certain speed. it has been customary in the past tocause the starting winding to be disconnected by means such as acentrifugal device. Such centrifugal devices have generally consisted ofa collar mounted on a shaft, means biasing the collar to close a pair ofcontacts, and By weight means which is adapted to overcome the biasingmeans at a predetermined speed to pull the collar along the shaft andopen the contacts controlling the starting winding circuit. in order tomake the contacts open at a proper predetermined speed it was necessaryto devote great care to the longitudinal position of the motor shaft andthe attached centrifugal mechanism, since any deviation from the properposition would greatly change the force exerted by the spring andconsequently the speed at which the contacts would open. Also, arelatively large number of elements rotatable with the shaft have beenneeded in previous arrangements.

Another undesirable feature of previous designs has been the fact thatrubbing contact was inherent in the arrangement, since a rotating collarwas used to mechanically separate a pair of non-rotatable contacts, orelse a rotating collar and contact were separated from a stationarycontact. This feature of rubbing created wear, and the wear resulted ina change in spring tension and consequently a change in the speed atwhich the contacts opened.

in specialized types of motors, where the motor is closed to theatmosphere and a particular type of gaseous atmosphere is used in theinterior of the motor, it may well be that the gas will provedeleterious to electrical contacts. In previous constructions, wherevthe contacts were separated entirely by mechanical means, the exposureof the contacts to the atmosphere could not be avoided to a certainextent. It is proposed in the present invention to avoid by magneticmeans the necessity for mechanically moving the contacts, therebyavoiding the rubbing contact, the wear, the consequent sensitivity and,in specialized instances, the harm to the contacts from the atmospherewithin the motor.

It is, therefore, an object of this invention to provide improved meansoperable at a predetermined speed which will incorporate the advantagesset forth above.

Further objects and advantages of this invention wil become apparent andthe invention will be better understood by reference to the followingdescription and the accompanying drawing, and the features of noveltywhich characterize this invention will be pointed out with particularityin the claims annexed to and forming a part of this specification.

nited States Patent "0- Patented June 19, 1956 This invention, in itsbroadest aspect, provides a substantially circular member of magneticmaterial movably secured to a rotatable member; the magnetic material isbiased to a position which is not vertical to the rotatable member whenit is at rest. When the rotatable member comes up to speed the magneticmember will, under the influence of centrifugal force, move to aposition in a vertical plane to the axis of rotation of the rotatablepart. A permanent magnet is mounted so that when the disc becomesvertical to the rotatable part the magnet is pulled downwardly. Amovable contact is adapted to be moved by the magnet so that when themagnet is pulled downwardly the contacts, which are normally closed,will be opened. The magnet will move downwardly toward the magneticmember because of the magnetic attraction which arises between them.Thus, as long as the rotatable part is rotating fast enough to maintainthe magnetic member in a plane vertical to the axis of rotation, themagnet will be attracted to the magnetic memher and the contacts will beseparated. in a modification of this embodiment, the permanent magnetand the contacts are hermetically enclosed in a non-magnetic housing sothat the contacts will not be affected by the atmosphere surroundingthis housing.

In the drawing, Figure l is a side view, partly in crosssection andpartly cut away, of an electric motor embodying the improved speedsensitive device of this invention;

Figure 2 is an enlarged side view of the improved speed sensitive deviceshown in Figure 1;

Figure 3 is a front view, partly in cross section, of the improved meansshown in Figure 2; and

Figure 4 is a fragmentary front view, partly in cross section, of amodification of the improved speed sensitive means of this invention.

Referring now to Figure l of the drawing, shown a small single phasealternating current of the type having a starting winding (not shown)which is disconnected when a predetermined speed is attained. Motor 1 isenclosed in a housing member 2 of a generally cylindrical shape whoseends are closed by end shields 3 and 4 which are secured to member 2 byany standard means. Motor 1 drives a shaft 5 which is rotatablysupported by bearings (not shown) contained within hub 6 of end shield3- and hub 7 of end shield 4. A casing member 8 having an annular flange9 may be secured to end shield 4 by any well known means such asthreaded members 10 extending through flange a into end shield 4. Shaft5 extends through end shield 4 into casing member 8 as shown at 11. Theimproved speed responsive apparatus of this invention is containedWithin the casing 8.

Referring now to Figures 1, 2 and 3, one embodiment f the invention willbe described. A substantially round disc-like member 12 is secured toshaft 5 at end 11 by any preferred means. As shown in the presentembodiment, this has been effected by providing oppositely disposedkeyways 13 in shaft 5, with projections 14 of disc 12 fitting within thekeyways so as to hold the disc to the shaft. This relatively simpleholding means may be effected by stamping out openings 15 and 16 in thecenter of the disc, placing the disc over shaft 5, inserting a screwdriver (not shown) or some other like tool in the opening 15, anddeforming the strip 17 as shown so as to cause projections 14 to enterkeyways 13. A leaf spring 18, secured to disc 12 at 19 by any preferredmeans suchas welding and to shaft 5 by means such as projection 20extending into and secured within shaft 5, is adapted to bias disc 12 toa canted position when shaft 5 is stationary. Opening 16 in disc 12 ismade sufficiently large so that the disc may be canted a considerableamount without interference between it and shaft 5. Disc 1?. is

there is motor 1 further provided with cut away portions 21 atdiametrically opposite points on its periphery for a purpose to behereafter explained.

A terminal board member 22 is secured within casing 8 to end shield 4.This may be effected by any preferred means; in the embodiment shown,threaded members 23, 24 and 25, whose secondary functions will beexplained below, have been given the primary function of securing board22 to end shield 4. A stationary contact 26 is mechanically andelectrically secured to a small bracket member 27 which in turn isfastened to board 22 by threaded member 23. A relatively long leafspring member 28 is firmly secured by nut 29 and screw 30 to a bracket31 which in turn is fastened to terminal board 22 by threaded members24. A movable contact member 32 is electrically and mechanically securedto leaf spring 28 and limits the upward movement thereof by engagementwith stationary contact 26. Secured to the end of leaf spring 28 by anydesired means, such as a nut 33 and a bolt 34, is a permanent magnet 35.The dimensions of the various elements are such that when disc 12 is ina position vertical to the axis of rotation of shaft permanent magnet 35is directly above the outer periphery of the disc. Downward movement ofleaf spring 28 is limited by a stop member 36 which may be secured to orformed integral with bracket 37 which is in turn secured to board 22 bythreaded members 25. That part of threaded member 23 which extends intoend shield 4 is adapted for use as one electrical terminal and either ofthreaded members 24 may likewise be adapted for use as a secondterminal. Thus, by attaching properly connected leads (not shown) to thestart winding (not shown) of the motor, it is possible to cause contacts26 and 32 to determine whether the start winding will be energized. Inthe embodiment shown, members 23 and 24 are insulated from end shield 4to prevent a short in the circuit to the starting winding. It will beapparent, however, that casing 8 may be eliminated and that the improvedspeed responsive means of this invention may be wholly mounted withinhousing member 2 and end shields 3 and 4 without departing from thescope of this invention. In such an event, there would be no need forany measures, such as explained hereabove, for preventing short circuitsbetween the terminal members 23 and 24. By the same token, any desiredterminal arrangement may be used, since such arrangements are notcritical insofar as the invention is concerned.

The operation of the improved mechanism of this invention will now bedescribed. When shaft 5 is brought up r to a predetermined speed ofrotation, centrifugal force will overcome the action of spring 18, anddisc 12 will move to a vertical position with respect to the axis ofrotation of shaft 5, as shown in dotted outline in Figures 2 and 3. Whendisc 12 is in this position it is directly beneath permanent magnet 35.The magnet therefore tends to attract the magnetic disc toward it. Sincethe disc is fastened so that no such movement is possible, magnet 35 ispulled down toward the disc taking with it leaf spring 28 and movablecontact 32 until its movement is stopped by stop member 36 as shown indotted outline in Figures 2 and 3. Movement of contact 32 in a downwarddirection opens the circuit controlled by the contacts 26 and 32 and thestart winding of the motor will therefore be deenergized. This state ofaffairs will continue to exist as long as the speed of rotation of shaft5 is high enough to keep disc 12 in the vertical position. When thespeed of rotation of shaft 5 drops below the predetermined point, spring18 will return disc 12 to its canted position. Magnetic attractionbetween the disc and magnet 35 will cease, and spring 28 will returnmagnet 35 and contact 32 to their upward position where the energizationto the start winding will again be completed through contacts 26 and 32.

It will be seen that the necessity for securing disc 12 to shaft 5 sothat the disc may pivot results in the fact that the two opposite pointson the periphery of the disc which are in line with an extension of theaxis on which the disc pivots will remain substantially in the verticalplane when the disc is canted to cause its other parts to be out ofaxial alignment with magnet 35. Thus, even when the disc is in itscanted position these points would be directly beneath magnet 35 if thedisc should stop its rotation at a point 90 removed from the positionshown in the figures. For this reason, cut-away portions 21 have beenprovided so that even if the disc should stop in such a position therewould be no magnetic material directly beneath magnet 35 to causecontacts 32 and 26 to be separated. When the speed of rotation is suchthat the disc moves to its vertical position, the location of each ofcut away portion 21 directly beneath magnet 35 will be of such shortduration that they will have no effect on the magnetic action betweendisc 12 and magnet 35, and magnet 35 will remain properly in itsdownward position so long as disc 12 is in a vertical position.

In the modification shown in Figure 4, a board member 38 of insulatingmaterial has fastened to it by means of a nut 39 and screw 40 a casing41 formed of non-magnetic electrically conductive material. Insulation,denoted by numerals 42 and 43, is provided so that casing 41 is entirelyinsulated from screw 40. The head 44 of screw 40 forms a stationarycontact which is adapted to engage with a movable contact 45 in order toclose an electrical circuit, as explained in Figures 1, 2 and 3. End 46of screw 40 is adapted to act as the terminal of the stationary contact44, and the casing 41 forms the terminal for the movable contact 45.Movable contact 45 is electrically and mechanically secured to apermanent magnet 47 which has an opening 48 formed therein toaccommodate a helical spring 49 which is seated at one end on the bottom50 of casing 41 and at the other end on the top 51 of recess 48. Spring49 normally biases the permanent magnet 47 and the movable contact 45upwardly so that contacts 44 and 45 are in engagement to complete thecircuit.

As in Figures 1, 2 and 3 a tiltable disc 12 is provided which assumes avertical position directly beneath magnet 47 at a predetermined speed ofrotation. When disc 32 assumes its vertical position as shown in Figure4 a magnetic attraction arises between it and magnet 47. Since disc 12does not move upwardly, magnet 47 comes down against the action ofspring 49 thereby opening the contacts 44 and 45 and deenergizing thecircuit which was completed through them. When disc 12 returns to acanted position away from magnet 47 spring 49 will again close thecontacts 44 and 45. Casing 41 is preferably constructed so that theelements within it are hermetically sealed from the outside atmosphere.The embodiment of Figure 4 is particularly useful and desirable where itis necessary that the mechanism be operated in an atmosphere which mighthave deleterious eifects upon the surfaces of contacts 44 and 45. Insuch an event, this arrangement permits the contacts to be used with complete efficiency in such an atmosphere without being affected by it.

It will be seen that this invention provides a speed responsive devicewherein the necessity of rubbing contact is completely obviated byeliminating the mechanical operation of the movable contact by arotating part. In addition, the size of the permanent magnet willnormally be such that there is no need whatsover for accurate axialadjustment of the position of disc 12. Because of this, a reliable andprecise determination of the speed of actuation is possible without thedifliculties of assembly which were previously inherent.

It will be understood that the housing and easing members describedhereabove are for purposes of illustration, and may be eliminated or.modified without departing from the scope of the invention.

While this invention has been explained by describing particularembodiments thereof, it will be apparent that improvements andmodifications may be made without departing from the scope of theinvention as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Speed responsive apparatus comprising a substantially circular memberpivotably secured to a rotatable part so as to be rotatable therewithand biased to a canted position with respect to the axis of rotation ofsaid part when said part is at rest, said member being movable to avertical position by centrifugal force at a predetermined speed ofrotation, and magnetic means located substantially in the same plane assaid member when the same is in its vertical position and beyond theperiphery of said member, said magnetic means being biased away fromsaid member and being susceptible to magnetic force between it and saidmember to overcome said bias and move toward said member when it is inits vertical position, said member having a pair of diametricallyopposite peripheral cut-away portions located in line with the pivotalaxis of said member thereby to preclude movement of said magnetic meanstoward said member below said predetermined speed of rotation.

2. Speed responsive apparatus comprising a substantially circular memberpivotably secured to a rotatable part so as to be rotatable therewith,spring means biasing said member to a canted position with respect tothe axis of rotation of said part when said part is at rest, said memberbeing movable to a vertical position by centrifugal force at apredetermined speed of rotation, a permanent magnet locatedsubstantially in the same plane as said member when the same is in itsvertical position and beyond the periphery of said member, second springmeans biasing said magnet away from said member, said magnet beingsusceptible to magnetic attraction between it and said member toovercome said second spring means when said member is in its verticalposition, stop means associated with said magnet to limit its traveltoward said member, said member having a pair of diametrically oppositeperipheral cut-away portions located in line with the pivotal axis ofsaid member thereby to preclude movement of said permanent magnet towardsaid member below said predetermined speed of rotation.

3. Speed responsive apparatus for controlling an electrical circuitcomprising a disc-like member pivotably secured to a rotatable shaft soas to be rotatable therewith, spring means biasing said member to acanted position with respect to the axis of rotation of said shaft whensaid shaft is at rest, said member being movable to a vertical positionby centrifugal force at a predetermined speed of rotation, a permanentmagnet located substantially in the same plane as said member when thesame is in its vertical position and beyond the periphery of saidmember, a leaf spring immovably secured at one end and secured to saidmagnet at the other end, said leaf spring being arranged to bias saidmagnet away from said member, said magnet being susceptible to magneticattraction between it and said member to overcome the bias of said leafspring when said member is in its vertical position, contact meanscontrolling said circuit and operable to open said circuit when the biasof said leaf spring is overcome, a stop member positioned between saiddisc member and said leaf spring to limit the travel of said magnettoward said disc member, said member having a pair of diametricallyopposite peripheral cutaway portions located in line with the pivotalaxis of said member thereby to preclude movement of said magnet towardsaid member below said predetermined speed of rotation.

4. Speed responsive apparatus for controlling an electrical circuitcomprising a disclike member pivotably secured to a rotatable shaft soas to be rotatable therewith, a leaf spring engaging said shaft at oneend and secured to said member at the other end thereby to bias saidmember to a canted position with respect to the axis of rotation of saidshaft when said shaft is at rest, said member being movable to avertical position by centrifugal force at a predetermined speed ofrotation, permanent magnet located substantially in the same plane assaid member when the same is in its vertical position and beyond theperiphery of said member, a second leaf spring immovably secured at oneend and secured to said magnet at the other end, said second leaf springbeing arranged to bias said magnet away from said member, said magnetbeing susceptible to magnetic attraction between it and said member toovercome the bias of said second leaf spring when said member is in itsvertical position, a first electrical contact secured to said secondleaf spring intermediate its ends, a second electrical contact immovablyarranged to engage said first contact when said magnet is biased awayfrom said member and thereby complete said electrical circuit, saidfirst contact being arranged to move away from said second contact whensaid magnet moves toward said member thereby to disconnect saidelectrical circuit, a stop member arranged between said disc member andsaid second leaf spring thereby to limit the travel of said magnet andsaid second leaf spring toward said disc member, said disc member havinga pair of diametrically opposite peripheral cutaway portions located inline with the pivotal axis of said disc member thereby to precludemovement of said magnet toward said disc member below said predeterminedspeed of rotation.

5. Speed responsive apparatus for controlling an electrical circuitcomprising a disc-like member pivotably secured to a rotatable shaft soas to be rotatable therewith, a leaf spring engaging said shaft at oneend and secured to said member at the other end thereby to bias saidmember to a canted position with respect to the axis of rotation of saidshaft when said shaft is at rest, said member being movable to avertical position by centrifugal force at a predetermined speed ofrotation, a permanent magnet located substantially in the same plane assaid member when the same is in its vertical position and beyond theperiphery of said member, an electrically conductive non-magnetic casinghermetically enclosing said magnet, a coil spring seated at one endagainst an inner surface of said casing and at the other end againstsaid magnet thereby to bias said magnet away from said member, a firstelectrical contact secured to said magnet, a second electrical contactmechanically secured to and electrically insulated from said casing,said first contact being arranged to engage said second contact whensaid magnet is in biased position thereby to complete said electricalcircuit, said magnet being susceptible to magnetic attraction between itand said member to overcome the bias of said coil spring when saidmember is in its vertical position whereby said magnet moves toward saidmember and said first contact separates from said second contact tobreak said circuit.

6. Speed responsive apparatus for controlling an electrical circuitcomprising a disc-like member pivotably secured to a rotatable shaft soas to be rotatable therewith, spring means biasing said member to acanted position with respect to the axis of rotation of said shaft whensaid shaft is at rest, said member being movable to a vertical positionby centrifugal force at a predetermined speed of rotation, a permanentmagnet located substantially in the same plane as said member when thesame is in its vertical position and beyond the periphery of saidmember, an electrically conductive non-magnetic casing hermeticallyinclosing said magnet, electrically conductive means within said casingin contact with said casing and with said magnet arranged to bias saidmagnet away from said member, an electrical contact within said casingand electrically insulated therefrom, said magnet being susceptible tomagnetic attraction between it and References Cited in the file of thispatent said member tr overcame said biasing means when said UNITEDSTATES PATENTS member is in its vertical position whereby said magnet 6moves towards said member, said magnet being arranged ,754 et July 1937to control electrical engagement of said contact and said 5 21215294Sept- 1940 casing.

